Writing about the instructions laid out in his will, Mr Buffett said his advice for the cash left to his wife was that 10 per cent should go to short-term government bonds and 90 per cent into a very low-cost S&P 500 index fund.

“I suggest Vanguard’s [S&P 500 index fund],” wrote Mr Buffett, adding that the long-term results from this policy would be superior to those attained by most investors, whether pension funds, institutions or individuals, that employed high-fee managers.